Effect Of Fe/mn/zn On Microstructure And Properties Of Copper-phosphorous Solder And Joints

Copper phosphorus solder has been widely used in aviation,aerospace,electronic appliances,etc.due to its low melting point,self-fluxing,low cost and high brazing joint strength.However,the inclusion of impurity elements in the solder manufacturing process is a key factor that affects the performance and quality of the solder.However,although researchers have pay much attention on the study of impurity elements,there are still no reports on the study of the impurity elements Fe,Mn,and Zn on the microstructure and properties of Cu-P solder and joints in my search fields.In this paper,the effects of Fe,Mn,and Zn elements on the microstructures and mechanical properties of the solders and joints were investigated by means of optical microscopy,scanning electron microscopy,energy spectrum analyzer,microhardness test,wettability test,tensile test,and differential thermal analysis.And the impact mechanism of the above elements was also preliminarily diseussed.Compared with B-CuP7 without Fe,the eutectic structure of B-CuP7 with Fe was obviously grown up,and Fe₂P and Fe₃P phases appeared.Meanwhile,the wetted area showed a downward trend.With the increase of Fe element,the microhardness of the solder rised.When the Fe content increased to 0.1wt.%,the tensile strength of the solder reached the maximum value.The microstructure of the brazing seam is not much different from the as-cast microstructure.However,when exceeding 0.1wt.%,the solder and joint tensile strength decreased.Obvious pores appeared at the tensile fracture of the welded joint,and the mechanical properties of the joint decreased.Therefore,the amount of Fe element in B-CuP7 cannot exceed 0.1 wt.%.Compared with B-CuP7 without Mn,the dendrite spacing of B-CuP7 with Mn added was significantly reduced,and secondary dendrite was closely packed.And??-Cu+Cu₃P?distribution was relatively uniform.Meanwhile,thespreading area showed a slow first and then fast downward trend.When Mn content was less than1.5wt%,the microhardness and tensile strength of the solder tend to improved.When the amount of Mn added exceeded 1.5 wt.%,black worm-like microstructures appeared,whose edges were rounded by bright white.Furthermore,new phases MnP and Mn₂P were detected by XRD.In addition,despite the increased tensile strength of the solder joint,it is still less than the B-CuP7 solder joint tensile strength.Therefore,the Mn mass fraction in B-CuP7 does not exceed 1.5%.The tensile strength of joints brazed with Mn decreased first and then increased,but it was still less than the tensile strength of B-CuP7 brazed joints.When the Mn content exceeded 1.5wt.%,the microstructure at the tensile fracture of the joint was significantly coarsened.Considering comprehensively,the mass fraction of Mn in B-CuP7 should not exceed1.5%.Compared with B-CuP7,the number of secondary dendritesa and the dendrite spacing of B-CuP7 solders with Zn added increased,and the gray-white lamellae boundaries in the microstructures became sharp with obvious edges.Moreover,the wetted area gradually increased,and the microhardness increased first and then decreased.When the mass fraction of Zn was 1.0%,the solder reached the maximum microhardness with a value of 249.6 HV.And the solder tensile strength gradually reduced with the riseing of the Zn content.As for the brazed joints,the tensile strength increased first and then decreased,When the Zn content was increased to more than 2.0wt.%,the tensile strength of the joint is reduced to less than that of the non-addition,and the river-like scattering textur at the tensile fracture became shallow and the mechanical properties were poor.Therefore,the Zn content in B-CuP7 should not exceed 2.0 wt.%to ensure good mechanical properties of the brazed joints.In summary,Fe,Mn,and Zn mainly affected the existence of inclusions,the types of phases generated,the formation of brittle phases,??-Cu+Cu₃P?morphology,and secondary dendrite size.The mass fraction of Fe,Mn,and Zn added in B-CuP7should not exceed 0.1%,1.5%,and 2.0%,respectively.